The present invention relates to the field of energy recovery, and more particularly, to the extraction of potential energy that exists in the form of excess pressure in natural gas pipelines.
Natural gas is typically transmitted in transmission pipelines at a pressure of 700 to 1000 psia. The gas pressure is reduced to 150 to 200 psia by pressure regulators and control valves at city gate stations for delivery to a distribution network where the pressure is again reduced to approximately 50 psia and supplied to consumers. However, the potential energy inherent in the excess gas pressure is lost in conventional pressure reduction devices, primarily in the form of waste heat.
One proposed solution to this problem of lost energy in natural gas pipelines is Stewart & Stevenson's recently developed energy recovery device referred to as the "Power Expander." When installed inline, high pressure gas passes through a nozzle in the Power Expander that directs the gas at an angle onto a reaction turbine wheel. The wheel is turned by the force of the gas, transmitting mechanical energy through an output shaft that is coupled to an induction generator.
When installed in a natural gas transmission line having an incoming pressure of 150 psia with a continuous flow of 21 million cubic feet per day and an outgoing pressure of 50 psia, the Power Expander produced an output of 382 hp that generated 250 kW at a 100 psi pressure reduction. Thus, this device produces approximately 3.82 hp that generates 2.5 kW per psi of gas pressure reduction, respectively.
It is an object of this invention to provide a method and apparatus for converting gas pressure to electricity by flowing gas under pressure sequentially into one of a plurality of downwardly opening receptacles in a liquid-filled vessel at a level where the hydrostatic pressure of the liquid equals the desired pressure reduction in the gas, to displace a portion of the liquid in the receptacle and create a buoyant force urging the receptacle upwardly and converting the buoyant force of the upwardly moving receptacles into rotary power.
It is a further object of this invention to provide an apparatus for converting gas pressure to useable power by using gas to displace liquid in downwardly facing buckets or receptacles carried by an endless drive chain and use the hydrostatic force of the liquid acting on the gas in the buckets to move the buckets upwardly to rotate the shaft of an electric generator.
It is a further object of this invention to provide an apparatus for producing power while reducing the pressure of gas in a pipeline, comprising a liquid-filled vessel having two vertical sections and two horizontal sections connecting the respective upper and lower ends of the vertical sections, a sprocket mounted for rotation with a horizontal output shaft in one of the horizontal sections, an idler pulley mounted for rotation in the other horizontal section, an endless drive chain encircling the sprocket and idler pulley, a plurality of open-ended receptacles carried by the drive chain, each receptacle being positioned on the chain for the open end of the receptacle to be facing downwardly as the receptacle moves upwardly with the drive chain and facing upwardly as the receptacles move downwardly with the chain, and a gas inlet at the bottom of the vessel positioned for at least a portion of the gas entering the vessel to enter the downwardly facing open ends of the buckets and displace liquid from the buckets and create a buoyant force urging the receptacles upwardly imparting rotation to the sprocket and the output shaft and reducing the pressure of the gas in the bucket, which gas is released to flow upwardly to the top of the vessel as the bucket is turned upside down as it travels over the sprocket, and an outlet for the gas at the top of the vessel.
It is still a further object of the present invention to provide a device for reducing the gas pressure in natural gas pipelines while significantly improving the amount of energy that may be recovered per psi of gas pressure reduction. Specifically, it is intended that the present invention will provide approximately 31.42 hp that will generate 22.14 kW per psi of gas pressure reduction, when operating to reduce an incoming pressure of 150 psia to an outgoing pressure of 50 psia.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification including the attached drawings and appended claims.